There are many types of systems that process, transport, or use a pressurized fluid. To ensure the safety of these types of systems, each such system typically includes a safety device designed to prevent the over-pressurization of the system. In an emergency situation, where the fluid in the system reaches an unsafe level, the pressure of the fluid acts on the safety device to create an opening to release fluid from the system. Venting fluid to the environment or a safety reservoir through the opening reduces the pressure in the system and prevents another portion of the system from failing due to the high pressure of the fluid.
Examples of commonly used safety devices include rupture disks and explosion panels. These safety devices can be attached to a pressurized system to expose a certain portion of the device to the pressurized fluid in the system. The portion of the device exposed to the fluid is configured to rupture or tear when the fluid reaches a predetermined pressure. The tearing or rupture of the disk or panel creates an opening through which the pressurized fluid flows to reduce the pressure in the system. This type of safety device is, therefore, self-destructing and must be replaced after each use. Typically, to replace one of these safety devices, some disassembly of the system is needed so that the disk or panel can be properly engaged with the system.
Another type of safety device for a pressurized system is a pressure relief valve, which may be a reclosing valve or a non-reclosing valve. Typically, a spring, a pin, or a combination of a spring and pin, is used to hold a moving plug in sealing engagement with the housing of the device while connected to the pressurized system. When the pressure of the fluid reaches the predetermined safety level in such systems, the force exerted on the plug by the pressurized fluid overcomes the bias of the spring or exceeds the resistance of the pin that holds the plug in place. When either of these events occurs, the pressurized fluid moves the plug to expose an opening through which fluid may escape to relieve the pressure in the system. Reclosing valves will automatically reset once the pressurized fluid at the inlet of the device has reduced sufficiently for the spring or other mechanism to reseat the plug. Non-reclosing valves require that the device be manually reset so that the valve plug is re-engaged with the seal and, if necessary, the pin or other expendable component replaced.
As noted above, relief valves are known that use buckling pins, or breaking pins, to hold a sealing plug in sealing engagement to block the flow of a pressurized fluid. The pin release device prevents the plug from venting pressurized fluid until the output force exceeds a predetermined limit. Prior release devices have included a pin that is subject to a compressive force and that buckles according to Euler's Law when the output force reaches the predetermined limit or a shearing or tensile force that causes the breaking of the pin when the output force reaches the predetermined limit. Such a device is typically termed a “Buckling Pin Non Reclosing Pressure Relief Device.”
Buckling pins are carefully manufactured components configured to buckle at a particular predetermined compressive force. Breaking pins are carefully manufactured components configured to fail at a particular predetermined tensile or shear force. Such pins used for a pressure relief valve require considerable care and control during installation. Maintenance personnel must ensure that the pin is properly secured and tightened to properly bear the pressure exerted on the pressure relief valve. Failure to do so may result in untimely opening of the valve. A premature opening below the predetermined safety level leads to an unwanted downtime for the system, while a delayed opening above the predetermined safety level jeopardizes the physical integrity of the system. Another problem with a bare pin is that there is a risk of pin damage stemming from maintenance personnel having to contact the bare pin during installation or maintenance. This risk of pin damage is especially high for a fragile, low pressure bare pin.
As noted above, it order to properly function as a safety pressure relief device, it is important that the relief device vents at, or close to, the set pressure. Since buckling pins are designed to buckle at a predetermined compressive force, a pressure relief system must assure that force from the pressurized system is efficiently transferred to the buckling pin. In prior devices, forces from the pressurized system are often improperly transferred through the pressure relief device's structural system such that the compressive force experienced by the buckling pin is not an accurate representation of the actual force transmitted by the pressurized system. For example, forces transferred to the buckling pin from the pressurized system are often lost due to bending, friction between moving parts, and moments generated along the path of transmitted force.
In some pressure relief devices, and particularly those having a low set pressure, mishandling and improper installation of the underlying buckling pin can interfere with the accuracy of the set pressure of the device. For example, buckling pins can be dangerously overloaded during the pre-assembly and installation process such that the pin activates at a much lower pressure than desired during use.
In light of the foregoing, there is a need for a pressure relief apparatus that (1) efficiently and accurately transfers force between the pressurized fluid and the buckling pin, (2) assures that pins are not overloaded during the pre-assembly and installation process, and (3) can provide for resistance to back pressure while maintaining proper positive pressure venting as a pressure relief device.